The present invention relates to a noise making device using a piezoelectric transducer, and more particularly to a piezoelectric audible signal generator incorporating a three-electrode piezoelectric transducer, an amplifier, a phase shifter and a feedback loop.
A known, typical piezoelectric noise making device has, as illustrated in FIG. 1, a three-electrode piezoelectric transducer X.sub.1 having a resilient thin metal plate 1 as a ground electrode, piezoelectric plate 2 and driving electrode 3 wherein the driving electrode 3 is connected to a collector of a transistor Q.sub.1 while a feedback electrode 4 is connected through a resistor R.sub.3 to a base of the transistor Q.sub.1.
However, the known noise making device using the feedback type piezoelectric transducer produces a less sound pressure than the expected value which is inferred theoretically from the case of a two-electrode piezoelectric transducer without a feedback electrode. An attempt has been made to overcome the disadvantage by utilizing a transformer to heighten a voltage of a power supply, which, however, directs to a large scale of the device and does not meet with industrial, commercial requirements.